1. Field of the Invention
The present invention relates to a buckle device, which, in a seat belt device for a vehicle, maintains a state in which a webbing belt restrains the body of a vehicle occupant.
2. Description of the Related Art
A buckle device forms a portion of a seat belt device for restraining, by an elongated webbing belt, the body of a vehicle occupant who is seated in a seat of a vehicle. The buckle device is locked by passing a latch through a hole formed in a tongue plate provided at the webbing belt in a state in which the tongue plate is inserted into a case of the buckle device, so as to apply the webbing belt to the vehicle occupant.
Among such buckle devices, there are those of the type which are provided with a detecting means for detecting whether the latch is engaged with the tongue plate. The detecting means detects unlocked states, such as the tongue plate not being completely inserted into the case or the latch not being engaged even if the tongue plate is completely inserted. Notice can be given of the locked state by, for example, having an indicator be lit only at times when the buckle device is in a locked state.
One example of such a detecting means is a structure using a so-called Hall sensor. (For an example of a structure using a Hall sensor, refer to Japanese Patent Application Laid-Open (JP-A) No. 10-230815, whose counterpart U.S. patent is U.S. Pat. No. 5,742,986.) The Hall sensor is an electronic part whose electrical resistance value varies in accordance with the intensity of a magnetic field by application of the so-called Hall effect.
In such a detecting means utilizing a Hall sensor, for example, the Hall sensor is disposed so as to oppose the latch along the moving direction of the latch within the buckle body, and a magnet (a permanent magnet) is disposed at the side of the Hall sensor which is opposite the side at which the latch is provided. The latch is formed of a magnetic body of iron or the like. The Hall sensor detects changes in the intensity of the magnetic field of the magnet with respect to the Hall sensor, which changes are caused by the latch approaching or moving away from the Hall sensor and the magnet when the latch is engaged with the tongue plate and locked or when this locking is released. Due to the Hall sensor detecting such changes, it can be detected whether or not the latch is engaged with the tongue plate and locked.
However, buckle devices, in which whether or not the tongue plate is locked is detected by using a Hall sensor, have the following problems.
First, as described above, the Hall sensor is of a structure in which the intensity of a magnetic field is fed out as an electric signal by using the Hall effect. Accordingly, when the magnetic force of the magnet, which is the source of the magnetic field, deteriorates due to the passage of time or the like, there is the possibility that, regardless of whether the latch has approached the Hall sensor, the Hall sensor can only detect a magnetic field of an intensity which is the same as that if the latch had not approached the Hall sensor. Thus, a structure utilizing a Hall sensor lacks reliability for use in a buckle device which is used over a relatively long period of time.
Second, Hall sensors generally have poor temperature characteristics. They thus lack reliability for use in buckle devices which are provided in vehicles in which temperature variations are great.
In view of the aforementioned, an object of the present invention is to provide a buckle device in which it can be detected whether or not a tongue plate inserted into a case is locked, and in which the reliability of such detection is high.
In order to solve the above-described problems, a buckle device of the present invention comprises: a tongue plate; a buckle main body; a movable latch interlocking with the tongue plate which is inserted into the buckle main body; at least one movable magnetic body related to interlock operation; and a sensor operable for detecting movement of the magnetic body, wherein the sensor includes a magnetoresistance element utilizing an anisotropic magnetoresistance effect, and a bias magnet.
A belt buckle device of the present invention comprises: a belt having a tongue plate at one end of the belt; a buckle main body; a latch which releasably interlocks with the tongue plate within the buckle main body; and a sensor for detecting interlock operation, the sensor including a magnetoresistance element utilizing an anisotropic magnetoresistance effect, and a bias magnet.
A seat belt device for a vehicle of the present invention comprises: a flexible belt, one end of the flexible belt being mounted one of directly and indirectly to one of a vehicle body and a seat, the other end of the flexible belt having a tongue plate; a buckle main body, one end of the buckle main body being mounted one of directly and indirectly to one of the vehicle body and the seat, the other end of the buckle main body having an opening; a movable latch for interlocking with a tongue plate which is inserted into the opening of the buckle main body; and a sensor operable for detecting interlocking operation, the sensor including a magnetoresistance element utilizing an anisotropic magnetoresistance effect, and a bias magnet.